Lubricating the points to be lubricated in a reciprocating piston engine, for instance a four-stroke engine, is done as a rule by pressure-recirculation lubrication, in which the lubricating oil is carried from a reservoir to the various points to be lubricated via a pump and distribution lines. The bearings between the connecting rod and the crankshaft on the one hand and between the crankshaft and the engine block on the other are supplied with lubricating oil via corresponding bores in the crankshaft and crankcase, while the lubrication of the piston/cylinder tube units is done through the injection oil present in the crankcase. Lubricating the piston/cylinder tube unit by means of injection oil has the disadvantage that as a rule substantially more lubricating oil than necessary is delivered to the point to be lubricated. Oil stripper rings must therefore be provided, which increase the friction between the cylinder and the cylinder tube and thus lower the efficiency of the engine.
In two-stroke internal combustion engines, besides pressure-recirculation lubrication with external scavenging processes, mixture lubrication, especially with crankcase scavenging, is employed. In this lubrication system, the lubricating oil is exposed to the fuel. Together with the fuel, the lubrication oil is atomized and reaches the points to be lubricated along with the air aspirated by the engine. One disadvantage of this lubricating system is that the lubricant can be delivered to the various points to be lubricated only in an uncontrolled fashion. There is also the disadvantage that by far the majority of the lubricant exposed to the fuel is expelled again, via the combustion chamber of the engine, without contributing to lubricating the points to be lubricated. Hence this lubrication system requires increased consumption of lubricant and results in major environmental pollution.
It is also known in two-stroke internal combustion engines to deliver the lubricating oil as a function of engine load and/or engine speed. In this so-called separate lubricating system, the delivery of oil, depending on the engine model, is made to the fuel, to the aspirated air, or directly to the points to be lubricated via liquid pressure oil. With this lubricating system, accurate dosing of the delivered quantity of lubricating oil is impossible, or can be done only with major effort. It is therefore known to deliver the lubricating oil to the point to be lubricated in increments, or in other words at time intervals. That has the disadvantage, however, that good lubricating action or even excess lubrication is attained only after the delivery of lubricant, and by the next time lubricant is delivered the lubrication decreases sharply. Since very slight quantities of lubricant are often all that is necessary, it is impossible with this lubricating system to achieve a precisely dosed delivery of lubricant.
One process for targeted delivery of lubricant in a two-stroke internal combustion engine is known from H. W. Bonsch, Der schnell laufende Zweitakt-Motor [The High-Speed Two-Stroke Engine] Motor Buch Verlag 1982, page 140, in which each piston/cylinder tube unit is supplied by means of pressure oil via a bore. The crankshaft bearing for each cylinder is likewise lubricated via pressure oil. Another process of supplying lubricant to crankshaft bearings is disclosed in SAE Paper 85157, published in 1985. In this process, the lubricant is drawn into the respective bearings by negative pressure via riser lines. For the sake of assuring reliable lubrication provision is also made to blow air into the riser line by means of the excess pressure in the piston housing. In this process, precise dosing of the quantities of lubricant needed at the various points to be lubricated is not possible.
The object of the invention is to create a process for supplying the points to be lubricated in a reciprocating piston engine, with which an at least approximately exactly dosed, targeted delivery of lubricant is possible.